Self-clinching nuts and pierce nuts of the type disclosed herein generally include a projecting central pilot portion, which may be used to pierce a metal panel or plate to which the fastener is to be attached and the pilot portion is then received through the pierced panel opening. The nut is then attached to the metal panel by a die member which forms a mechanical interlock between the nut and the panel. The panel may be deformed by the die member into grooves in the nut or the nut may be deformed to entrap panel metal.
Many pierce nuts are used by the automotive industry to assemble cars in which many components of various kinds are attached to metal plates or panels. Pierce nuts are used to attach lamps and sheet metal parts, for example, to the vehicle. When such parts are attached, screws or bolts are threaded into the threaded hole in the nut and a bolt or screw is tightened with rotating tools, such as a torque wrench, at prescribed torque values. The clinch nut must therefore have sufficient anti-torque or rotation resistance (the force that keeps the pierce nut from rotating on the metal plate when a bolt is threaded into the nut and tightened) to bind it to the metal panel. After a component is attached to the clinch nut on a metal plate, external forces, such as vibration and tensile forces applied to the automobile, act upon the nuts from the pull-through direction attempting to pull the nuts from the metal plate to which they are attached. Therefore, each clinch nut must have sufficient pull-through resistance (the force that keeps the nut from coming out of the metal plate when the nut and a bolt are engaged and the force is applied to the bolt perpendicular to the metal plate) that is stronger than these external forces.
As stated, the torque value of the rotating tool or torque wrench is predetermined, such that the rotational resistance of the clinch nut in the panel should be sufficient to resist this torque value, but the external forces applied to the automobile often cannot be forecast. Therefore, the aforementioned pull-through resistance must be relatively high.
When pierce or clinch nuts are being driven into metal plates, the pierce nuts are supplied to the installation tooling continuously through an outlet of a supply device, such as a hopper. Thus, it would be preferred if the shape of the pierce or clinch nut permits free variance of the attachment direction on the surface of the metal plate. In other words, the shape of the pierce nut should permit free variation of the direction that each pierce nut emerges from the outlet of the hopper. In cases in which pierce nuts are to be driven into a metal panel in a number of locations, the pierce nuts should be shaped so that the direction of the pierce nut outlet can be freely varied to suit the installation operation.
Further, in the automotive industry, which utilizes many pierce nuts, there is a trend toward thinner metal panels or plates to reduce the weight of each car. Thus, it is necessary to have pierce or clinch nuts shaped to provide the necessary rotation resistance and greater pull-out and pull-through resistance, even when used on thin metal plates. When, for example, it is necessary to achieve pull-out resistance in excess of 200 kg. and sufficient rotation resistance to withstand the tightening torque when applied by a torque wrench with a 0.6 mm. plate and the bolt or screw meets resistance during engagement of the nut, existing pierce nuts of the type described above cannot consistently satisfy these requirements.
As described above, a pierce or clinch nut is typically attached to a metal panel or plate in conjunction with an installation die commonly referred to as a die button. The die button includes one or more projecting lips or protrusions configured to be received in the nut groove or grooves. When the pierce or clinch nut has an annular groove, the die button includes an annular lip or protrusion configured to be received in the annular groove of the nut. When the self-attaching nut is a pierce nut, the die button typically includes a shearing edge or surface which cooperates with an outside surface of the pilot portion of the pierce nut to pierce an opening in the panel. The pierce nut pilot is then received through the pierced panel opening and the lip or protrusion of the die button then deforms the panel into interlocking relation with the nut groove or grooves. However, as described above, this mechanical interlock must be sufficient to withstand the torque which may be applied to the nut when a bolt is cross-threaded in the nut and tightened and the nut must have sufficient pull-out and pull-through resistance for commercial applications.
With existing die buttons, the material around the pierced panel opening is deformed by the two surfaces formed by the cylindrical outer surface of the circular lip or protrusion on the die button and the annular die face that is perpendicular to this outer surface and by the outside wall of the annular groove in the pierce nut when the panel metal is deformed into the annular groove. Thus, when insufficient panel metal is deformed by the annular lip of the die button, insufficient panel metal is inserted into the groove and it is not possible to increase the mechanical interlock between the panel metal and the groove to achieve the required pull-out strength. When the panel or plate is particularly thin, the volume of panel metal deformed in the groove is insufficient and the nut falls off the plate.
Certain problems developed with the manufacture and installation of the embodiments of the self-attaching nut disclosed in the above-identified U.S. parent application, Ser. No. 011,439. As will be understood by those skilled in the art, the forming punch used to form the annular groove of the self-attaching nut has an annular lip which conforms to the shape of the bottom of the groove. In the embodiments disclosed, the die lip includes an end face having depressions conforming to the shape of the protuberances, which are aligned in the midportion of the bottom wall of the groove. However, when forming oil adheres to the depressions in the end of the forming punch, the oil cannot escape during formation of the groove. This results in resistance and incomplete forming of the protuberances; however, the protuberances are essential to radial deformation of the metal panel during installation as described in the above-identified parent application. Thus, the pierce nuts disclosed in the above-identified parent patent application does not provide sufficient retention or torque resistance on the panel using conventional forming techniques.
Further, the wall of the pilot portion in the embodiment disclosed in the parent application is very thin at the bottom of the groove because the groove inner wall is inclined outwardly. As described in the above-identified parent application, during installation of the nut in a panel, the panel metal is deformed radially inwardly and driven against the inner portion of the annular wall of the pilot, which may result in distortion of the female thread in the nut bore. This has resulted in binding of the screw or bolt as it is threaded into the nut bore following installation of the nut.
Finally, the projecting annular lip of the die button used to install the nut must be relatively thin at the tip as the lip includes an outer annular concave filet which forms the panel metal in the groove as described in the above-referenced parent patent application. This results in weakening of the annular lip and shortened die button life, which is not acceptable, particularly in mass production applications. Thus, there was a need for improvement of the design of the embodiments of the self-attaching fastener disclosed in the above-referenced parent patent application.
The improved self-attaching nut fastener disclosed in this application significantly improves the life of the die button and permits the full formation of the protuberances using conventional forming techniques, thus improving the manufacturing and installation processes of the pierce nut. Further, the self-clenching fastener or pierce nut may be reliably attached to a thin metal panel or plate providing sufficient pull-out strength and rotational resistance without distortion of the threads in the nut bore.